Railroad tracks and cross ties are conventionally supported on beds of stone ballast. The stone ballast provides a firm foundation for the tracks and the cross ties. Further, the spaces between the ballast stones allow for proper drainage of the track bed area. Proper drainage is important to prevent erosion of the track bed area and deterioration of the wooden cross ties, both of which ultimately lead to an unsafe track condition. Over time, the space between the individual stones of the ballast becomes fouled with dirt, debris, and so called "fines" from the wearing down of the individual ballast stones. Fouling of the ballast prevents proper drainage, leading to premature deterioration of the wooden cross ties and weakening of the track bed.
It has become commonplace for railroad companies to periodically remove the ballast from the shoulders of the railroad track beds, clean it, and redispose the cleaned ballast on the shoulders. Such periodic cleaning has been found to restore proper drainage, even when the ballast between the cross ties is not removed and cleaned. The stone ballast is typically removed from the shoulder of the track bed shoulder, carried to a vibrating screen where the stone ballast is separated from the dirt, debris, and fines. The cleaned ballast is then replaced on the bed shoulder. The residual dirt and debris is deposited on either side of the track bed or is stored in a hopper car for removal from the cleaning site.
A problem exists with conventional ballast cleaning machines in that such machines are designed to remove the fouled ballast, clean it, and replace the cleaned ballast onto the track bed immediately as the cleaned ballast emerges from the vibrating screen. At any given time, the ballast that is being redeployed on the track bed is that ballast that was dug up a few minutes prior for cleaning. The quantity of ballast that is redeployed is that ballast that is presently available, without regard to the quantity of ballast that may properly be needed at that particular portion of the track bed.
It is desired, however, that the ballast that is replaced at any given point along the track bed be the correct amount to adequately support the bed and to promote good drainage. The correct amount is not uniform over a given length of track. While it might be assumed that simply removing an amount of ballast, cleaning it and replacing the same amount onto the track bed would be satisfactory, this is frequently not the case. The amount of cleaned ballast available from the cleaning apparatus may be too much or too little for the track bed. Neither condition is presently accommodated by conventional ballast cleaning machines.
The correct amount of ballast is a function of track bed conditions and the operating cycle of the ballast cleaning machine. For instance, when the cleaning operation first commences, there is often not enough cleaned ballast available from the vibrating screen or other cleaning apparatus to put down an adequate quantity of cleaned ballast on the track bed. In this case, supplemental clean ballast is needed. There are also stretches of the track bed that have too little ballast to be removed to be able to lay down an adequate amount of cleaned ballast using only that ballast which has been removed from the track bed and cleaned. In this case also, supplemental clean ballast is needed in order to ensure that an adequate quantity of ballast is returned to the track bed. Conversely, there are stretches of track bed that have an excessive amount of ballast that is removed for cleaning. Only a portion of the removed ballast need be replaced on the track bed in order to have an adequate amount of ballast. Presently, such excess cleaned ballast is wasted by dumping it alongside the track bed. It would be advantageous if the excess portion of the cleaned ballast could be stored on board the ballast cleaning machine for later discharge on the track bed as desired. It would be especially helpful if the excess ballast was available for redeployment along those portions of the track bed where an inadequate amount of fouled ballast is available for removal, cleaning, and redeployment.
The above conditions create a need to have both a ready supply of supplemental ballast for discharge onto the track bed when the supply of freshly cleaned ballast is inadequate and a storage capacity to be able to temporarily store a quantity of excess freshly cleaned ballast that has been removed from the track bed. Conventional ballast cleaning machines do not have the integral storage capacity to convey a sufficient quantity of new ballast to the cleaning site and to have it readily accessible for deploying on the track bed and to store excess ballast as it is cleaned.
Hoppers that function to receive cleaned ballast from the cleaning mechanism and funnel the clean ballast to chutes for immediate redistribution on the track bed shoulder have been used. Examples can be found in U.S. Pat. Nos. 2,775,438, 2,900,745, 3,900,392, and 4,203,493. Such hoppers are utilized as transitory devices that redeploy the cleaned ballast onto the track bed through the chutes attached to the hopper as soon as the ballast is received in the hopper.
A hopper of simple design, integrated with the ballast cleaning machine, that requires a minimum of ballast conveying apparatus and yet has a substantial ballast storage capacity such that ballast is not wasted and is always ready to be distributed along the track shoulder would meet a long felt need in the railroad track maintenance industry.